Prevalence of Intestinal Parasitosis in Guinea: Systematic Review of the Literature and Meta-Analysis

Background: Intestinal parasitosis constitute a major public health issue, particularly in sub-tropical and tropical areas. Even though they are classified as neglected tropical diseases, no national study has been carried out recently in Guinea to estimate the prevalence of intestinal parasitosis. Objective: A systematic review and meta-analysis aimed to determine the overall prevalence of intestinal parasitosis in Guinea. Method: The PRISMA method was used to perform a systematic review and meta-analysis. The studies carried out in order to study intestinal parasitosis in Guinea and published between 2010 and 2020 were searched in online public databases. The prevalence of parasitosis was calculated by a random-effects meta-analysis. Subgroup comparisons were performed using Q-tests. Statistical analyses were performed with the R software. This review was registered with PROSPERO under the identification number CRD42022349743. Results: 69 studies were selected out of 1230 studies identified in online public databases. The meta-analysis involved 44,186 people with an overall prevalence of intestinal parasitic infections of 52%. Conclusions: This is the first study in Guinea to assess the prevalence of intestinal parasitic infections in different regions of the country. It was found that intestinal parasitosis are a real health problem in Guinea, hence, the need to put in place national strategies for regular control.


Introduction
Intestinal parasitic infections are widespread in the world, with school-aged children being the most affected, with prevalences in some geographic areas of more than 50% [1]. According to the World Health Organization (WHO), in the world, more than 1.5 billion people are infected by intestinal parasites, and 450 million are seriously ill, with an estimated mortality rate of 155,000 cases per year [2]. The promiscuity and lack of hygiene associated with poverty favor their expansion. In some regions of the world, particularly in sub-tropical and tropical areas, intestinal parasitic infections are endemic and remain one of the leading causes of increased morbidity and mortality, justifying the mobilization of resources and actions aimed at their control and eradication [3,4].
Developing countries are the most affected by intestinal parasitic infections, particularly in areas such as sub-Saharan Africa, South and Central America, China, and East Asia [1,5]. This situation constitutes an obstacle to socio-economic development [6]. Intestinal parasitic infections are caused by both helminths and protozoans. Soil-transmitted helminths include, among others, Ascaris lumbricoides, responsible for ascariasis; Ancylostoma duodenale, responsible for hookworm infection; and Trichuris trichiura, responsible for trichocephalosis [5]. Among the water-transmitted helminths, Schistosoma mansoni,

Documentary Search Strategy
A systematic review of the literature and a meta-analysis were carried out using the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) method [18]. We searched in the PubMed/Medline, Google Scholar, and ResearchGate databases (for peer-reviewed journal articles) and in the Library of Gamal Abdel Nasser University (UGAN) in Conakry (for dissertations or theses of graduate students in the departments of medicine, pharmacy, and biomedical sciences) to compile all the studies carried out on intestinal parasitosis in Guinea and published between 2010 and 2020. Two reasons motivated the choice of this period: (i) Theses prior to 2010 were not accessible in the database of the Library of Gamal Abdel Nasser University in Conakry, and although the search was done in a digital catalog, only the papers formats of these dissertations were accessible in the library of the UGAN.; (ii) The National NTD Control Program, which defines national strategic guidelines, began after 2010.

Study Selection Criteria
Criteria were established for eligibility before beginning the search, as follows: Inclusion criteria: Articles that failed to report the number of study participants and number of cases

Search Strategy
The articles and theses/dissertations selected were read and analyzed in accordance with a reading grid, and the extracted data included: (i) name of authors; (ii) diploma obtained as a result of the study in the case of theses/dissertations (MD: medical doctor; PharmD: pharmacy doctor; master or MSc: master in sciences), and the reference number of the study; (iii) year of publication (year of publication by the editor or year of submission of the thesis to the university library); (iv) year of observation (period of beginning of inclusions or selection of the study population); (v) age range of the study population (according to age, the study population was divided into 5 groups: children between 0 and 5 years old, children between 0 and 17 years old, adults, mixed population (children and adults), and pregnant women); (vi) study setting; (vii) study site (area corresponding to the place of residence of the population included in the study. For the analysis of the study site, the districts were grouped by natural regions (Conakry, Lower Guinea, Middle Guinea, Upper Guinea, and Forest Guinea). Conakry was distinguished from Lower Guinea to highlight its cosmopolitan character and the fact that it was the only city in the country with an institute of medicine and pharmacy, since independence until 2006. Lower Guinea (20% of the area), is a maritime region characterized by high rainfall; Middle Guinea (18%) is a region of mountains and many rivers, Upper Guinea (22%) is the driest region in the country, Forest Guinea (40%) has a humid subtropical climate [16]; (viii) type of laboratory techniques: standard direct microscopic examination, direct microscopic examination after special stains and the concentration or staining/discoloration techniques performed (formol-ether, Kato-Katz, Willis, Ziehl -Neelsen) were listed; (ix) overall prevalence (any parasite); (x) type of parasites and the number of cases observed.
The prevalence of each of the most frequent parasitosis in the literature was retrieved over three periods: before 2010 (Period 1 (P1)), between 2010 and 2013 (Period 2 (P2)), and from 2014 to 2020 (Period 3 (P3)). These periods were chosen considering the application of the NHDP policy (Table 1).

Data Extraction
Studies were screened independently by two authors, first based on titles and abstracts. The full texts of papers identified as being potentially relevant for inclusion were retrieved and independently assessed by the same collaborators. Data extraction format for the pooled prevalence was facilitated using a Microsoft Excel sheet where data pertaining to the authors' names, publication year, study design, study setting, study area, region, technique of stool examination, sample size, and prevalence of intestinal parasitic infection were listed.

Statistical Analysis
The prevalence of parasitosis was calculated by a random-effects meta-analysis (heterogeneity between studies was expected). A logistic regression model with random intercept was used to estimate prevalence, with logit transformation. Confidence intervals of the estimates for each study were calculated with the Clopper-Pearson method (exact binomial interval). Subgroup comparisons were performed using Q-tests. The general significance level was set at a p-value below 0.05. Statistical analyses were performed with the R software version 4.0.5 [19]. The R code used for the analysis and the database were added as Supplementary File S1.

Protocols and Registration
This systematic review and meta-analysis were registered on PROSPERO under the registration number CRD42022349743 and can be accessed at https://www.crd.york.ac.uk/ PROSPERO (accessed on 28 July 2022).

Results
Characteristics of the Included Articles A total of 1230 studies were initially identified in the queried databases. Overall, 1128 studies were excluded during the first selection phase according to the following reasons: exclusion of articles published before 2010, dissertations or theses submitted at the library before 2010, publications not related to intestinal parasitosis, and duplicates. Out of the 102 publications or documents, after a second selection phase, 69 studies met the study criteria ( Figure 1). erogeneity between studies was expected). A logistic regression model with random tercept was used to estimate prevalence, with logit transformation. Confidence interv of the estimates for each study were calculated with the Clopper-Pearson method (ex binomial interval). Subgroup comparisons were performed using Q-tests. The general s nificance level was set at a p-value below 0.05. Statistical analyses were performed w the R software version 4.0.5 [19]. The R code used for the analysis and the database w added as Supplementary File S1.

Protocols and Registration
This systematic review and meta-analysis were registered on PROSPERO under registration number CRD42022349743 and can be accessed https://www.crd.york.ac.uk/PROSPERO (accessed on 28 July 2022).

Characteristics of the Included Articles
A total of 1230 studies were initially identified in the queried databases. Overall, 11 studies were excluded during the first selection phase according to the following reaso exclusion of articles published before 2010, dissertations or theses submitted at the libra before 2010, publications not related to intestinal parasitosis, and duplicates. Out of 102 publications or documents, after a second selection phase, 69 studies met the stu criteria ( Figure 1). In total, 100% of selected studies were cross-sectional, and 68% described the f quency of intestinal parasitosis in people consulting a health care structure; 32% were p formed in institutions such as schools, orphanages, universities, or jails. Parasitologi examination techniques were not described in 10 studies. In the remaining 59 studies microscopic examination of fresh stools was performed, as this is the most common used laboratory test for stool sample analysis. This standard examination was follow In total, 100% of selected studies were cross-sectional, and 68% described the frequency of intestinal parasitosis in people consulting a health care structure; 32% were performed in institutions such as schools, orphanages, universities, or jails. Parasitological examination techniques were not described in 10 studies. In the remaining 59 studies, a microscopic examination of fresh stools was performed, as this is the most commonly used laboratory test for stool sample analysis. This standard examination was followed by a modified Ziehl-Neelsen staining technique in only two studies or by the Kato-Katz technique in ten studies ( Table 2).  (6), T. trichiura (7) A, D Assoumani M., 2010, PharmD [22] 4 Children (           The studies were carried out in the natural regions of Guinea as follows: 34 in Conakry, 8 in Lower Guinea, 5 in Middle Guinea, 4 in Upper Guinea, 16 in Forest Guinea, and 1 multicentric study in Conakry and Lower Guinea. Twelve studies included children aged 0-5 years; twenty studies included children of less than 18 years old; twenty-seven included a mixed population (children and adults); and ten included only pregnant women (Table 2). Ten studies were carried out in P1, seventeen in P2, and forty-two in P3 (Table 2).

Pooled Prevalence of Intestinal Parasitic Infections in Guinea
The meta-analysis involved 44,186 people with an overall prevalence of intestinal parasitic infections of 52% (95 % CI: 43, 61) (Figure 2). A substantial heterogeneity was observed in the estimation of this pooled prevalence (I2 = 99%, p = 0). The studies were carried out in the natural regions of Guinea as follows: 34 in Conakry, 8 in Lower Guinea, 5 in Middle Guinea, 4 in Upper Guinea, 16 in Forest Guinea, and 1 multicentric study in Conakry and Lower Guinea. Twelve studies included children aged 0-5 years; twenty studies included children of less than 18 years old; twenty-seven included a mixed population (children and adults); and ten included only pregnant women (Table 2). Ten studies were carried out in P1, seventeen in P2, and forty-two in P3 (Table 2).

Pooled Prevalence of Intestinal Parasitic Infections in Guinea
The meta-analysis involved 44,186 people with an overall prevalence of intestinal parasitic infections of 52% (95 % CI: 43, 61) (Figure 2). A substantial heterogeneity was observed in the estimation of this pooled prevalence (I2 = 99%, p = 0).

Analysis by Type of Population
According to the type of study, the population was divided into 5 groups: children from 0 to 17 years, children from 0 to 5 years, adults, mixed population (children and adults), and pregnant women (without taking into consideration the age). The overall prevalence of intestinal parasites among pregnant women was 66 % (95% CI: 32, 89), the group with the highest prevalence, followed by 62% of prevalence in the mixed population. The young children were less infected, with a prevalence of 37 % (95 % CI: 26, 50) when compared to adults (Figure 4). The differences in prevalence between these subgroups were not statistically significant. A. lumbricoides was the parasite more frequently found in pregnant women (11%) and children (17%). S. mansoni was the parasite most frequently found in adults, with a prevalence of 14% (95 % CI: 11, 18).

Analysis by Study Setting
Subgroup analysis by setting showed a higher prevalence in studies conducted in the community than in those studies performed at health care centers, with a pooled prevalence of 65% (95% CI: 46, 80) and 46% (95% CI: 37, 56), respectively. However, this difference was not significant ( Figure 5).

Analysis by Region
There was no statistically significant difference in parasite prevalence according to the study region. However, when the association between the regions and the types of parasites was determined, the geographic occurrence of all types of parasites differed within the five regions, with the exception of S. stercoralis. Upper Guinea was the region with the highest prevalence of A. duodenale, Trichine, and H. nana. In addition, Upper Guinea together with Forest Guinea were the regions with the highest prevalence of S. mansoni. Middle Guinea had the highest prevalence of tapeworms. The prevalence of A. lumbricoides was higher in Conakry and Middle Guinea (Table 4). groups were not statistically significant. A. lumbricoides was the parasit found in pregnant women (11%) and children (17%). S. mansoni was frequently found in adults, with a prevalence of 14% (95 % CI: 11, 18).  community than in those studies performed at health care centers, with a pooled p lence of 65% (95% CI: 46, 80) and 46% (95% CI: 37, 56), respectively. However, this d ence was not significant (Figure 5).

Analysis by Period
Subgroup analysis of the proportions included in all selected studies showed a prevalence of intestinal parasitic infections as follows: 53% for P1 (before 2010), 61% for P2 (between 2010 and 2013), and 48% for P3 (2014 and after). This difference was not statistically significant. On the other hand, in Upper Guinea, Forest Guinea, and Conakry, a higher prevalence (all parasitosis combined) was noticed before 2014, but a significant decrease in prevalence during P3 was observed in all these localities (p < 0.01) ( Figure 6).

Other Parasites
Other parasites were detected, but the studies reporting them were very few, and they could not be included in the meta-analysis. Overall, 13 cases of H. diminuta were reported in 1 study (rank: 53), 51 cases of F. buski in 2 (rank: 20, 56), 67 C. parvum cases, and 1 case of Isospora infection were reported in 2 studies (rank: 31, 62), among immunodepressed patients, 12 cases of Balantidium were reported in three studies (rank: 40, 46, and 67).

Discussion
The present systematic review and meta-analysis assessed the prevalence of intestinal parasite infections in the general population of the country, establishing an overall prevalence of 52%. To our knowledge, this is the first study to provide a recent estimate of the prevalence of intestinal parasites in this country.
Before 2010, the prevalence of intestinal parasitosis in Guinea, according to the literature, was over 50% [4,88,89]. In this meta-analysis, this prevalence appears to vary from one study to another, sometimes over the same study period. However, even if a decrease in prevalence was observed here in P3 when compared to P1 or P2, prevalence remained high in all localities of the country. This slight decrease could be explained by the intensification of mass campaigns for the distribution of antiparasitic drugs in these localities [16]. However, the calculation of prevalence for P1 is based only on a limited number of studies that were available according to inclusion criteria and probably this is underestimating and not reflecting the real prevalence. In addition, it is well known that during the 2014-2016 Ebola virus disease (EVD) outbreak, routine health activities slowed down, including community-based activities such as deworming campaigns [3].
Transmission of A. lumbricoides is oro-faecal, so the predominance of the parasite could be attributed to its high rate of reinfection when compared to other soil-transmitted helminths [90]. Additionally, its eggs can remain dormant and tolerate adverse conditions in the soil for up to 10 years [91]. Hookworm infection is usually associated with bare skin contact with contaminated soil containing third-stage larvae [9]. S. mansoni infection is a consequence of contact with environmental freshwater infested with parasite larvae. Then, the disease is especially prevalent in communities lacking access to piped drinking water and adequate sanitation [92]. Particularly, S. mansoni infection was more prevalent in Forest Guinea. This is consistent with the report of the Health Minister of Guinea (2010), which indicated that this zone was the most affected by this infection between 2000 and 2005 [16].
The variation between regions and countries may be due to environmental factors such as temperature, humidity, rainfall, etc. In addition, differences in levels of sanitation should also be considered [97].
In addition, this study describes the prevalence of protozoans infecting the digestive tract such as E. histolytica and G. intestinalis. Concerning Cryptosporidium, this parasite was detected in 33% of patients infected with HIV, making it the most frequent parasitosis after ascariasis in this population. However, the presence of Cryptosporidium was not searched systematically since only two studies reported Ziehl-Neelsen staining as a specific diagnostic test [50,80].
In terms of the age of the population, the studies selected in this systematic review covered all age groups. Herein, the prevalence of intestinal parasites found in children less than 17 years old was 44%. When considering children under 5, the prevalence of intestinal parasites was 37%. This prevalence of intestinal parasites among under-five children was higher than that found in Saudi Arabia (17.7%) or Zambia (19.6%), lower than findings in Pakistan (52.8%), and slightly similar to the prevalence in Sudan (30%) [97,98]. Similar   were reported in preschoolers and schoolchildren [99]. Behavioral and social practices in children and their weak immune status, especially in under five, may account for the high frequency of intestinal parasitic infections [2,3,8]. With respect to pinworm prevalence, this was very low in children, in contrast with studies reporting this parasite as one of the most important intestinal pathogens in this group [100]. This could be explained by the fact that the identification of pinworms was performed only by microscopic examination of feces and not by the Scotch tape test, which is considered the gold standard for the diagnosis of E. vermicularis [101]. On the other hand, a prevalence of 66% of parasitic infections was found in pregnant women. This finding is similar to a prevalence of 66.7% reported in Burkina Faso [102]. In contrast, lower prevalences have been reported in Ghana (14.3%), Kenya (13.8%), or Ethiopia (27.32%) [103][104][105]. A. duodenale was among the most frequent type of parasite in this group. Infection by this parasite can lead pregnant women to severe anemia, and then there is an increased risk of morbidity and mortality for the mother and the baby after hookworm infections [105]. Maybe the calculation of prevalence for children and pregnant women was subject to bias considering that the detection of parasites is done systematically in these two groups. However, these results are consistent with WHO reports establishing that children and pregnant women are the most affected by soil-transmitted helminth infections [106].
All regions of Guinea presented prevalences of intestinal parasitic infections of more than 40% without significant differences. However, Upper Guinea was the region with the highest prevalence of A. duodenale, tapeworm, Trichine, and H. nana. Consistently, this region is considered with the highest degree of poverty [107]. On the other hand, in Upper Guinea, Forest Guinea, and Conakry, a high prevalence (all parasitosis combined) was noticed, but a significant decrease in prevalence during P3 was observed in all these localities.

Strengths and Limitations of the Study
A key strength of this systematic review and meta-analysis is that is the first to our knowledge to determine the pooled prevalence estimates of intestinal parasitic infections in Guinea. In addition, a rigorous search of several databases and other sources to identify eligible studies can also be considered one of the strengths of this review. On the other hand, one of the main limitations relates to a selection bias due to the fact that sampling in the majority of the studies was performed in healthcare structures since data from the general population in Guinea were limited and not available. The heterogeneity of the studies was also a limitation of the research.
Furthermore, concerning diagnostic tests, microscopic examination of fresh stools was the most commonly used method. In particular, techniques more adequate for the diagnosis of E. vermicularis and S. stercoralis, such as the Scotch tape test [100] and the Baermann [108], respectively, were not performed. Then, it is possible that some parasites were not routinely detected in clinical laboratories. WHO has recommended the Kato-Katz method as the best and most reliable diagnostic tool for the detection of human soil-transmitted helminths [109]. PCR would have been more sensitive in the identification and confirmation of several protozoans such as Cryptosporidium [110]. In addition, in all studies, only single stool sample tests were performed despite the recommendations suggesting at least three tests for the standard diagnosis [111]. Therefore, the prevalence was probably underestimated.
There was no adequate information on the distribution of prevalence according to sex, so it was not possible to evaluate whether the prevalence of intestinal parasitosis differed according to sex.
While the risk factors associated with pathogens could not be determined from the information provided in the selected studies, we suggest that they are likely to be related, in part, to factors such as socioeconomic status, access to potable water, and sanitation solutions. These factors were not explicitly described in many studies but are known as important predictors of intestinal parasitosis incidence in developing countries [10].

Conclusions
This is the first study in Guinea to assess the prevalence of intestinal parasitic infections in different regions of the country. It provides important data from 1989 until now, which may help in the conception and execution of public policies. We showed that intestinal parasitosis are a real health problem in Guinea, hence the need to put in place national strategies for regular control with a view to their eradication.
Prevention by deworming has been one of the most frequently applied strategies to fight against intestinal parasitosis. According to the WHO, large-scale preventive chemotherapy programs are required when the prevalence of any soil-transmitted helminth infection is higher than 20%, and this prevention is recommended twice a year when the baseline prevalence is over 50% [112]. Even if this strategy is one of the pillars of Guinea's national NTD program, deworming is administered in this country only once a year. Moreover, this problem also requires actions based on more effective long-term solutions such as supplying better sanitation, access to clean drinking water, urban cleaning, solid waste management, and provision of improved drainage and management of urban rainwater [10]. In the near future, further research in the following areas is needed: outcomes of preventive chemotherapy; identification of households at risk; the correlation between the intensity of infection and morbidity; effects of co-interventions such as nutritional, environmental, water, hygiene, or sanitation; compliance with large-scale preventive chemotherapy programs, and effects of health education.